What PHP 7 Changed

PHP 7.0 (2015) replaced the Zend Engine with PHPNG, roughly doubling performance and cutting memory use versus PHP 5.6. It added scalar type declarations (int, float, string, bool), return types, declare(strict_types=1), the ?? and <=> operators, anonymous classes, and turned most fatal errors into catchable Error exceptions under the new Throwable interface. Old mysql_* functions and ASP-style tags were removed.

All PHP 7 branches are end-of-life (7.4 ended in November 2022), so PHP 7 work today is mostly maintaining and upgrading legacy applications.

<?php
declare(strict_types=1);

function average(array $values): float
{
    if (count($values) === 0) {
        throw new InvalidArgumentException('Empty list');
    }
    return array_sum($values) / count($values);
}

try {
    undefined_function();
} catch (Error $e) {            // PHP 7: engine errors are catchable
    error_log($e->getMessage());
}

Common pitfalls

• Catching Exception and assuming it covers engine errors — Error is a separate branch of Throwable.
• Assuming PHP 7 code is still supported — no PHP 7 version receives security fixes from php.net.
• Mixing strict and coercive typing across files without realizing the setting is per file.

Key points

• PHP 7 brought a huge performance jump
• Scalar/return types and Throwable arrived in 7.0
• All PHP 7.x versions are end-of-life

Further reading: PHP manual: PHP 7.0 new features